Subject: Re: [PATCH 3/4] s390: enable text relative kallsyms for 64-bit targets

From: Heiko Carstens <[email-masked]>
Date: Wed, 20 Jan 2016 11:17:51 +0100

On Wed, Jan 20, 2016 at 11:04:24AM +0100, Ard Biesheuvel wrote:
> On 20 January 2016 at 10:43, Heiko Carstens <[email-masked]> wrote:
> > On Wed, Jan 20, 2016 at 10:05:37AM +0100, Ard Biesheuvel wrote:
> >> This enables the newly introduced text-relative kallsyms support when
> >> building 64-bit targets. This cuts the size of the kallsyms address
> >> table in half, reducing the memory footprint of the kernel .rodata
> >> section by about 250 KB for a defconfig build.
> >>
> >> Signed-off-by: Ard Biesheuvel <[email-masked]>
> >> ---
> >>
> >> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> >> index dbeeb3a049f2..588160fd1db0 100644
> >> --- a/arch/s390/Kconfig
> >> +++ b/arch/s390/Kconfig
> >> @@ -149,6 +149,7 @@ config S390
> >>       select HAVE_REGS_AND_STACK_ACCESS_API
> >>       select HAVE_SYSCALL_TRACEPOINTS
> >>       select HAVE_VIRT_CPU_ACCOUNTING
> >> +     select KALLSYMS_TEXT_RELATIVE if 64BIT
> >
> > Please remove the "if 64BIT" since s390 is always 64BIT in the meantime.
> > Tested on s390 and everything seems still to work ;)
> >
> > Acked-by: Heiko Carstens <[email-masked]>
> >
> 
> Thanks! Did you take a look at /proc/kallsyms, by any chance? It
> should look identical with and without these patches

Close to identical, since the generated code and offsets change a bit with
your new config option enabled and disabled. But only those parts that are
linked behind kernel/kallsyms.c.

However I did run a couple of ftrace, kprobes tests and enforced call
backtraces. Everything still works.

So it looks all good.